The correct statement is " A single bond, because they overlap orbitals to share one pair of electrons." A fluorine atom is unstable with 7 electrons in its valence shell and so needs one more electron to achieve stability. This is according to the octet rule which states that an atom will gain or lose electrons until there are 8 electrons in its valence shell. So each fluorine donates an electron to form a single pair and the
achieves a noble gas configuration.
For moles to grams would be the mole which is 7.9*10^-1 times the molar mass of argon